1. Field of the Invention
The present invention relates to photoresist polymers and photoresist compositions containing the same. In particular, the present invention relates to polycarbonate photoresist polymers and photoresist compositions comprising the same that are suitable for photolithography processes employing KrF, ArF, VUV, EUV and similar light sources.
2. Description of the Background Art
Recently, chemical amplification-type DUV photoresists have been investigated in order to increase sensitivity in minute image formation processes for preparing semiconductor devices. Such photoresists are prepared by blending a photoacid generator and matrix resin polymer having an acid labile group.
In a photolithography process, an exposure of photoresist to light of a particular wavelength generates an acid from the photoacid generator that is present in the photoresist. The photo generated acid causes the main chain or the branched chain of the resin to decompose or become cross-linked. In addition, the acid removes the acid labile group and changes the polarity of the photoresist in the exposed region. This polarity change creates a solubility difference between the exposed portion and the unexposed portion in a developing solution, thereby allowing a pattern formation. The resolution of the pattern that is formed depends on the wavelength of the light source, i.e., in general, a shorter wavelength allows formation of more minute patterns.
In general, a useful photoresist (hereinafter, abbreviated as xe2x80x9cPRxe2x80x9d) has a variety of desired characteristics, such as excellent etching resistance, heat resistance and adhesiveness. In addition, a photoresist should be easily developable in a commercially readily available developing solution, such as 2.38 wt % aqueous tetramethylammonium hydroxide (TMAH) solution. However, it is very difficult to synthesize a photoresist polymer that satisfies all of these requisites.
To solve some of the problems described above, there have been much research done on a resin having the high transparency at the wavelength of 193 nm and dry etching resistances similar to a Nobolac resin used in an i-line, for example, IBM has developed the following methacrylate copolymer resin of formula 2: 
wherein, R1, R2 and R3 are independently H or CH3.
In the resin of formula 2, the ratio of xe2x80x9cxxe2x80x9d must be increased in order to improve the dry etching resistance. However, if the amount of xe2x80x9cxxe2x80x9d is increased, hydrophilicity of the resin itself is reduced, therefore a minute pattern may fall down. In order to overcome such a disadvantage, hydrophilic monomers such as a methacrylic acid are copolymerized. However, in this case, a photoresist top loss may occur, and thus a special developing solution such as a diluted solution or a solution containing isopropylalcohol must be employed, instead of the currently used developing solution. In addition, if the resin does not contain a predetermined degree of the alicyclic compounds, it cannot satisfy the etching resistance.
On the other hand, photoresists of formulas 3 and 4 comprising polycarbonate have been developed. The resin of formula 3 is not a chemical amplification resist, and thus has inferior sensitivity and throughput. Accordingly, a large quantity of photoacid generator must be used. In addition, the resin comprises wholly aromatic compounds, and thus has poor optical transmissivity in the wavelength of 193 nm. As a result, the resin cannot be employed for the ArF lithography process. The resin of formula 4 can be utilized as the chemical amplification resist, and thus has excellent sensitivity. However, it also contains wholly aromatic compounds, and thus has poor optical transmissivity in the wavelength of 193 nm. Therefore, the resin of formula 4 cannot be used for the ArF lithography process: 
Accordingly, it is an object of the present invention to provide photoresist polymers which can be employed as ArF photoresists and methods for preparing the same.
Another object of the present invention is to provide photoresist compositions comprising such PR polymers.
Still another object of the present invention is to provide a semiconductor device produced by using the above described PR composition.